SIMV is a strategy to decrease lung injury. The most reliable trigger for small infants is a Graseby pressure capsule, since airway flow and pressure triggers become increasingly unreliable with decreasing weight. Even the capsule trigger has limitations: 1) proper positioning, and 2) infants can become "phase-locked" in active expiration caused by late triggering. Based on pilot data, we propose to: a. Use an acoustic respiratory motion sensor (ARMS), together with a Graseby capsule as an improved SIMV trigger for small infants. b. Bring this trigger to practice (Phase II). Specific Aims Phase I Demonstrate in 10 preterm infants the feasibility of using the combined ARMS and Graseby capsule signals to: 1. Improve the response time for the NPB Star-Synch trigger. 2. Detect active expiration. 3. Monitor synchronization quality. Phase II 1. Include 10 larger infants requiring SIMV to devise an improved trigger algorithm for infants of all birthweights. 2. Incorporate this algorithm into a prototype combined ARMS and pressure capsule trigger. 3. Quantify differences in response time and gas exchange between a) the prototype trigger and b) an NPB Star-Synch, in a blinded crossover study in 20 additional infants of all birthweights. 4. Develop production specifications for prototype trigger units for use in a multicenter collaborative trial (after Phase II). PROPOSED COMMERCIAL APPLICATION: Potential commercial applications include 1) an improved ventilator trigger for infants and adults, 2) a continuous monitor of the quality of synchronization , and 3) a detector of active expiration. Jaycor has provided IR&D funding for development of the prototype device and obtaining the pilot data.